Method for rolling tubular material stock in a stretch reducing mill

ABSTRACT

A method for rolling down tubular material in a rolling mill wherein in the vicinity of the starting sections and/or end sections of the tubular material normally having thickened portions a stepwise variation of the rotational speeds is provided at the roll stands deforming these sections, said stepwise variation of said rotational speeds required for rolling the central section of the tubular material.

Elite Stats tet Plieifier et al. Feb. 29, 1972 [54] METHOD FUR ROLLINGTUBULAR MATERIAL STOCK KN A STRETCH Referemes Cit d REDUQNG MILL UNITEDSTATES PATENTS Inventors: Gel'd Pfeiflell'; Horst Billel', both Of Mul-2 t Z 4 X heimkuhr; Claus y, oberhausen; Ab 3,036,180 3mm 23mg; /23 redSchmitz, Mulheim-Ruhr, 0f Geran gggix: many 3,308,644 3/1967 Voin Dorp..72/249 [73] Assignee: Mannesmannrohren-Werke Gmbl-l, Dusseldorf,Germany Primary Examiner-Milton S. Mehr Attorney-Burgess, Dinklage &Sprung [22] Filed: July 1, 1969 [211 App]. No.: 838,384 [57] ABSTRACT IA method for rolling down tubular material in a rolling mill [30]Foreign Application priority Dam herein in the vicinity of the startingsections and/or end sections of the tubular material normally havingthickened pory 5, 1968 Germany 17 52 713-8 tions a stepwise variation oftherotational speeds is provided at the roll stands deforming thesesections, said stepwise varia- [52] US. Cl ..72/205, 72/208, 72/367, i fSaid rotational Speeds required f li the central 72/234 section of thetubular material. [51] Int. Cl ..B2lb 17/00 [58] Field of Search..72/205 234, 249, 208 7 Claims, 8 Drawing Figures PATENIEDFEBZQ I9723,645,121

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METHOD FOR ROLLING TUBULAR MATERIAL STOCK TN A STRETCH REDUCING MILLTubular material is reduced in its diameter in a rolling mill without aninternal die in a plurality of consecutive stand locations. In additionto this diameter reduction generally, a change in the wall thickness isalso effected, the rate of which depends on the stress conditionexisting in the rolled product. The stress condition in the rolledproduct which can be defined by the related longitudinal tension (K Lthe longitudinal force acting on the tubular cross section,

F tubular cross section,

k,= the mean tensile strength of the material of the rolled product),

is influenced by the stepwise change in the rotational speeds of theindividual stand locations. The more the longitudinal tension X isinfluenced by the stepwise change in the rotational speeds, the thinnerthe wall of the reduced tubular material will be. In order to thusobtain a desired wall thickness, a predetermined rotational speedsequence must be set in the rolling mill which yields the longitudinaltension required at the individual stand locations.

In conventional methods for rolling down tubular material thelongitudinal tension at the beginning and at the end of the tubularmaterial does not nonsequentially rise and fall between zero and thepredetermined rate with the preset rotational speed sequence, butstepwise. A tension rise as per definition is present in a stand in theevent that the longitudinal tension between the stand location m+l andthe stand location m is greater than the longitudinal tension betweenthe stand location in and the stand location m-l. A tension fall ispresent in a stand location k in the event that the longitudinal tensionbetween the stand location k+l and the stand location k is smaller thanthe longitudinal tension between the stand location k and the standlocation k-l. At the initial section of the tubular material thelongitudinal tension thus is decreased, whereas at the rearward sectionof the tubular material entering the first stand locations thelongitudinal tension is increased. It follows therefrom that the forwardsection and the rearward section of the tubular material to be reducedare subjected to a lower longitudinal tension than required for thedesired wall thickness variation. The predetermined rating of thelongitudinal tension and thus the desired wall thickness variation isachieved in the central portion of the tubular material only. The frontend and the rear end of the tubular material are thickened tubularpieces and are cut off as waste, a necessary result of the method.

It is an object of the invention to provide a method for rolling downtubular material in a rolling mill wherein the thickened front sectionof the tubular material is substantially shortened at least as comparedwith the front section of the tubular material thickened in theconventional methods.

A further object of the invention is to also substantially shorten thethickened rear section of the tubular material at least as compared withthe thickened rear section of the tubular material obtained by the priorart methods.

According to this invention, a stepwise variation of the rotationalspeeds is provided for rolling down tubular material in a rolling millin the vicinity of the front sections and/or rear sections of thetubular material normally having thickened portions at the standsdeforming these sections, said stepwise variation of the rotationalspeeds being greater than the stepwise variation of the rotationalspeeds required for rolling the central section of the tubular material.

This method is conveniently provided such that as far as the frontsection of the tubular material is concerned, the rotational speeds ofthe rolls at a plurality of stand locations 1 through m are decreasedprior to the entry of the front section of the tubular material relativeto the rotational speed sequence when the rolling mill is filled, thepercentage in the rotational speed decrease being greatest at the firststand location and decreasing with the increasing number of the standlocation, and that then when the front section of the tubular materialenters the reducing rolling mill the decreased rotational speeds of theindividual stand locations are increased again dependent on the passingof the front section of the tubular material through a plurality ofstand locations to the speed sequence with filled rolling material. Theincrease of the decreased rotational speeds can be effected inincrements or continuously at the stand locations which the frontsection has passed.

This invention furthermore contemplates that the percentage in theincrease of the rotational speeds to the rotational speeds with filledrolling mill is effected uniformly at all stand locations through whichthe front section of the tubular material passes. The rotational speedsof the stands through which the front section of the tubular materialpasses can be respectively increased in such a manner that they receivethe same percentage in the rotational speed decrease as the ultimatestand location rolling the front end of the tubular material.

Since the speed differentials of the stand locations effective astension diminishing upon entry of the front section of the tubularmaterial are greater by the rotational speed decrease than later uponrolling the central section of the tubular material where the standlocations are effective as stand locations maintaining the tensionconstant, the thickened front section of the tubular material can begreatly shortened. The speed differentials can even be selectedsufficiently large so that there is no point on the pressed surface ofthe caliber having the same speed as the tubular material. In this casethe roll slides in all contacting points on the tubular material due toits higher circumferential speed of the caliber relative to the tubularmaterial. By increasing the speed differentials for rolls alreadyslipping by an increase of the frictional work applied to the tubularmaterial the longitudinal tension in the tension decreasing stands canbe increased to a predetermined limit which can be determined by tests.

The memod according to the invention will be discussed in greater detailhereinafter, for the front section of the tubular material, withreference to the accompanying drawings.

FIG. 1 is adiagrammatic illustration of a rolling mill with the tubularmaterial entering, said rolling mill being operated according toconventional practice, the longitudinal tension occuring in the tubularmaterial being indicated;

FIG. 2 an illustration similar to FIG. 1 of the rolling mill illustratedthere with the tubular material having passed further into the rollingmill;

FIG. 3 an illustration of the rotational speed decrease and rotationalspeed increase at the individual stand locations or a rolling milloperating according to the method of this invention.

FIG. 4 is a diagrammatic illustration of a rolling mill operated inaccordance with the conventional method in the filled state with thelongitudinal tension existing in the tubular material;

FIG. 5 is a diagrammatic illustration of the rolling mill illustrated inFIG. 4 with outcoming tubular material, the longitudinal tensionexisting in the tubular material being illustrated;

FIG. 6 is an illustration of the speed reduction and speed increase inthe individual stand locations of a rolling mill in accordance with themethod of this invention;

FIG. 7 is an illustration of the speed reduction in the individual standlocations of a rolling mill in accordance with a variant of the methodof this invention.

In the rolling mill illustrated in FIG. 1 the tension increase iseffected in the stand locations 1 and 2, whereas the tension decrease iseffected in the stand locations 5 and 6 for the rotational speedsequence set. The longitudinal tension is constant between the standlocations 2 and 3 on the one side and the stand locations 3 and 4 on theother side. The stand location 3 located in the central tubular sectionthus is a stand location maintaining the tension constant.

As illustrated in FIG. 2 the tension decrease has shifted with theadvancing of the front section of the tubular material from the standlocations 5, 6 via the stand locations 6, 7 to the stand locations 7, 8.The stand locations 5, 6 have turned into stand locations maintainingthe tension constant with unaltered rotational speeds.

Since in the conventional method the front section of the tubularmaterial is rolled with a longitudinal tension during the entire passingthrough the stand, said longitudinal tension being below thelongitudinal tension required for the desired wall thickness, the wallthickness of the front section of the tubular material is thicker thanthe wall thickness of the central section of the tubular material. Thelength of the thickened front section of the tubular material depends onthe number of the stand locations which are required for the stepwisetension decrease. In FIGS. 1 and 2 the length of the front section is atleast equal to the spacing of two adjacent stand locations.

In order to substantially shorten this thickened front section,according to this invention the rotational speeds of the individualstand locations are decreased prior to the entry of the tubularmaterial, as is illustrated in FIG. 3. In the drawing 11 stand locationsare illustrated. The percentage in the rotational speed decrease fromthe entry of the tubular material relative to the rotational speed witha filled rolling mill amounts to 5 percent between the individual standlocations, so that rotational speed decrease of the stand location 1 is50 percent, that of stand location 2 is 45 percent etc., and finallythat of stand location 11 is percent. The increments in the decrease andthe number m of the stand locations with decreased speed is dependent onthe minimum and maximum rating of the longitudinal tension required forshortening the thickened front section of the tubular material and ofthe control range of the motors of the stand locations, in particular ofthe first stand location, i.e., the stand location number must beselected such that for a predetermined stepwise variation of the speeddecrease the speed decrease of the first stand location is within thecontrol range of the coupled motor or engine. When specifying thestepwise variation of the rotational speeds between the adjacent standsit must be observed that it is not selected at too large a value becauseotherwise a tearing off of the tubular material is effected.

When the tubular material now enters the rolling mill, an increasedlongitudinal tension is exerted on the front section due to thepercentage in the stepwise speed reduction at the stand locations 1 to1 1. This front section of the tubular material has been illustrated inFIG. 3 as a full drawn beam.

In phase I the front section extends across the stand locations 1 towith the speed reduction in increments of respectively 5 percent from 50percent at stand location I to 30 percent at the stand location 5. Inphase II the front section of the tubular material has passed standlocation 1. The speed reduction of stand location 1 has been raised tothe speed reduction of stand location 2. In phase III the front sectionof the tubular material has passed through stand location 2, the speedreduction of which is increased together with the speed reduction ofstand location 1 to the speed reduction of stand location 3, namely to40 percent. With the front section of the tubular material furtheradvancing the speed reductions are increased in an according manner inphases IV to X, so that finally in phase XI all stand locations havebeen increased to the speeds of the filled rolling mill. In thediagrammatic illustration of the individual phases it will be noted thatthe central section of the tubular material is not subjected to anyincreased tension during the speed increase, since the stands rollingthe central section of the tubular material are not operated relative toone another with speeds of unequal increments in their percentagerelative to the speeds with the rolling mill filled, but with rotationalspeeds of equal increments in their percentage.

The problem of substantially shortening the thickened section of thetubular material for the rear sections of the tubular material isconveniently solved in the following manner, there being twopossibilities:

In the first of these possibilities the problem is solved in that withthe rolling mill filled, the roll speed of all stands 2 in number)participating in the deformation of the tubular material are reducedrelative to the speed sequence used for rolling the central section ofthe tubular material, the percentage in the speed reduction at allstands being equal; thereafter when the rear section of the tubularmaterial enters the sequence of stands 1 through n of the rolling millthe reduced speeds of the stands 2 through 7 are increased dependent onthe passing of the rear section of the tubular material through thestands 1 through n in such a manner that the percentage in the speedreduction in the vicinity of the rear section of the tubular materialdecreases with an increasing number of stand locations to the stand n,and that the central section of the tubular material is rolled in standsthe percentage of speed reduction of which is equal.

Stands 1 thus maintains the overall reduction; stand 2 is increased onlyonce in the speed; stand 3 is increased in' the speed twice etc., up tothe stands n through p which are increased n minus once and therebyreach the initial speeds again. The decrease and increase of the speedscan be effected continuously or in increments. The number n of thesequence of stands in which the rolling speeds are reduced can bedetermined on the basis of tests.

A feature of the invention contemplates that the percentage increase ofthe rotational speeds of the stands which roll the central section ofthe tubular material is effected uniformly. This invention furthermorecontemplates that the rotational speeds at the stand locations 1 throughn are maintained after the rear section of the tubular material has leftthe rolling mill for the initially described method for shortening thethickened front section of the tubular material.

Since the speed differentials of the stand locations operating tensionincreasing upon entry of the rear section of the tubular material aregreater by the speed reduction than when rolling the central portion ofthe tubular material when the stand Iocations are operating as standlocations maintaining the tension constant, the thickened rear sectionof the tubular materiaI can be greatly shortened. The rotational speeddifferentials can even be selected sufficiently large so that there isno point on the pressed surface of the caliber which has the same speed.In this case the roll slips in all contacting points on the tubularmaterial as a result of its circumferential speed lower relative to thetubular material. By increasing the speed differentials for rollsalready slipping the longitudinal tension can be increased in thetension decreasing stands by increasing the frictional work applied tothe tubular material within a predetermined limit determined by tests.

This method is explained in greater detail hereinafter in referring toFIGS. 3 to 6.

In the rolling mill illustrated in FIG. 4 the tension buildup iseffected in stand locations 1 and 2, whereas the tension decrease iseffected in stand locations 7 and 8 for the preset rotational speedsequence. The longitudinal tension is constant between stand locations 5and 6 on the one side and stand locations 6 and 7 on the other side.Stand location 6 disposed in the central section of the tubular materialthus is a stand location maintaining constant tension.

As illustrated in FIG. 5, the tension buildup has varied with thetubular material leaving the mill as compared to the condition with themill filled, so that not the stand locations 1 and 2, but the standlocations 3 and 4 are stand locations building up tension.

Since in the prior art methods the rear section of the tubular materialis rolled with a longitudinal tension during the entire passing throughthe stand, said longitudinal tension being below the longitudinaltension required for the rolled wall thickness, the wall thickness ofthe rear section of the tubular material will be thicker than the wallthickness of the central section of the tubular material. The length ofthe thickened rear section of the tubular material depends on the numberof stand locations which is required for the incremental tension builtup. In FIG. 4 and 5 the length of the rear section is at least equal tothe spacing of two adjacent stand locations.

In order to now substantially shorten this thickened rear section,according to a feature of this invention the rotational speeds of theindividual stand locations are reduced prior to entry of the rearsection of the tubular material, starting from the rotational speedsequence for the deformation of the central section of the tubularmaterial, as illustrated in FIG. 6. In

the drawings, 24 stand locations have been illustrated. The

amount of the reduction depends on the minimum and maximum rating of thelongitudinal tension required for the shortening of the thickened rearsection of the tubular material, of the diameter reduction sequenceemployed (increments of the diameter reduction from one stand to theother), and of the control range of the motors or engines of the standlocations.

In the drawings thepercentage rotational speed reduction has beenselected with 50 percent for all 24 stands prior to entry of the rearsection of the tubular material into the rolling mill. Upon entry of therear section of the tubular material into the first stand the rotationalspeeds are increased by 5 percent from stand .2 to 24, i.e., a tubularsection results between stand 1 and 2 which is subjected to an increasedlongitudinal tension of the differential of the rotational speeds of 50percent minus 45 percent, or 5 percent. The exact time the rotationalspeed is increased is determined by the length of the rear section ofthe tubular material which has not yet entered the rolling mill, whichwill normally be 1 to 5 stand spacings, in considering the time requiredfor balancing the speed increase. In the drawing this length is 3 standspacings. Upon entry of the rear section of the tubular material in thesecond stand the rotational speeds are increased by 5 percent from stand3 to stand 24, again the time required for balancing the speed increasehaving to be considered so that the speed reduction amounts to 40percent for these stands, whereas it amounts to 45 percent for thesecond stand and 50 percent for the first stand. In FIG. 6 the rearsection of the tubular material on which an increased longitudinaltension is exerted is characterized as a beam drawn in full lines. Inphase I the longitudinal section subject to an increased longitudinaltension extends from stand 1 to 2, the stands 2 to 24 having a speedreduction of 45 percent and stand 1 having a speed reduction of 50percent. In the phase II stand 1 is reduced in its speed by 50 percent,stand 2 by 45 percent and stands 3 to 24 by 40 percent. With furtheradvancing rear section of the tubular material the speed reduction isaccordingly cancelled until in phase XIII the stand locations II to 24have been stepped up to the normal speed again. The quoted percentageshave been selected only for a better understanding in the givenmagnitude. The ratings suitable for performing the invention can bedetermined such that they are precalculated by means of the factorsdecisive for the amount of the speed reduction such as longitudinaltension required, diameter reduction sequence, control range of themotors or engines, which are then checked by test rolling and arecorrected. It will be noted from the diagrammatic illustration that thecentral section of the tubular material is not subjected to anyincreased tension for reduced speeds, since the stands rolling thecentral section of the tubular material are reduced by the samepercentage in their speed, i.e., that the ratio of the speeds for standswhich roll the central portion of the tubular material for the reducedcondition is equal to the ratio of the speeds in the nonreducedcondition.

FIG. 6 discloses that after the rear section of the tubular material hasleft the rolling mill the speed reductions still present at the standlocations I to 11 according to phase XIII are identical to phase Iaccording to FIG. 3 which illustrates the speed reduction in theindividual stand locations of a rolling mill for shortening thethickened front section of the tubular material. It will be notedtherefrom that the method of this invention permits the performing ofthe method for shortening the thickened front section of the tubularmaterial for the following tube or pipe without any particularpreparation.

In the second of these possibilities the problem is solved in that uponentry of the rear section of the tubular material in consecutive stands1 through q the associated roll speeds thereof are reduced dependent onthe passing of the rear section of the tubular material through thesestands such that in the vicinity of the rear section of the tubularmaterial the percentage in the speed reduction decreases with increasingstand location number, and that the central section of the tubularmaterial is rolled in stands with unaltered rotational speed. Thereduction of the rotational speeds can be effected continuously or inincrements. The rotational speeds of the stands which just roll the rearsection of the tubular material are at the same time reduced. The numberq of the consecutive stands in which the roll rotational speeds arereduced can be determined on the basis of tests.

This invention furthermore contemplates that the percentage in therotational speed reduction of the stand group respectively rolling therear section of the tubular material is effected uniformly.

Since the rotational speed differentials of the stand locationsoperating tension increasing upon entry of the rear section of thetubular material are greater by the speed reduction than when rollingthe central portion of the tubular material when the stand locationsoperate as stand locations maintaining constant tension, the thickenedrear section of the tubular material can be greatly shortened.

The amount of the reduction depends on the minimum and maximum rating ofthe longitudinal tension required for shortening the thickened rearsection of the tubular material, on the diameter reduction sequenceemployed (increments of the diameter reduction from one stand to theother), and on the control range of the engines or motors of the standlocations.

This method will be explained in closer detail hereinafter in referringto FIG. 7 of the accompanying drawings:

In FIG. 7, nine stand locations have been illustrated of a rolling mill.Starting from the rotational speed sequence for the deformation of thecentral portion of the tubular material the associated speed is reducedby 5 percent in stand 1 upon entry of the rear section of the tubularmaterial, the speed relationship for the speed of the stands I and 2thereby being varied such thatthe longitudinal tension existing in thetube or pipe is increased in (phase I J. The exact point at which therotational speed is reduced is determined by the length of the rearsection of the tube or pipe which has not yet entered the rolling mill,which is normally between one and live stand spacings, in consideringthe time required for balancing the speed reduction; in the drawing thislength is two stand spacings.

Upon entry of the rear section of the tubular material into the secondstand the rotational speeds are reduced from stand 1 and 2 by 5 percent,again the time required for balancing the rotational speed reductionhaving to be considered. In phase II the speed reduction for the firststand is 10 percent and for the second stand 5 percent. Thereby anincreased longitudinal tension results in a tubular section extendingfrom stand one to stand 3. When the rear section of the tubular materialadvances further through the rolling mill, the rotational speedreduction is accordingly repeated in such a manner that the respectivelylast stand in the stand group rolling the rear section of the tubularmaterial is subjected to the maximum speed reduction, for instance 15percent for stand 5 in phase VII, and the first stand of the stand groupis subjected to the minimum reduction, for instance 5 percent for stand7 in phase VII. In FIG. 7 the rear section of the tubular material onwhich an increased longitudinal tension is exerted is characterizedrespectively as a beam drawn in full lines in the individual phases. Thecited percentages have been selected merely for a better understandingin the instant magnitude. The ratings suitable for performing theinvention can be determined such that they are first precalculated bymeans of the practice decisive for the amount of the speed reduction,such as longitudinal tension required, diameter, reduction sequence,control range of the motors and engines, which are then checked by testrolling and are corrected. After the tube or pipe leaves the stands ofthe rolling mill, the rotational speeds for the stands which have beensubjected to a speed reduction are returned to those ratings for whichthey were set prior to the speed reduction for rolling the centralsection of the tubular material.

Naturally, the invention is in no way limited to the manners of carryingit out described herein by way of example. Variations may be resortedto, insofar as these changes come within the scope of the followingclaims.

What is claimed is:

l. A method of rolling down tubular material in a rolling mill in whichthe rolls of consecutive stands normally operate gradually increasingrotational speed, which comprises:

a stepwise reduction of the rotational roll speeds at a plurality ofroll stands prior to entry of the front section of the tubular material,the percentage of the rotational speed reduction being at a maximum atthe first stand location and decreasing at the subsequent stands; and

subsequently, upon entry of the front section of the tubular materialinto the rolling mill, an increase in speed of the individual standlocations, dependent on the passing of such front section through aplurality of stand locations, to the rotational speed sequence for afilled rolling mill,

so that the normally thickened front section of the tubular material issubstantially shortened.

2. A method as defined in claim 1, wherein the percentage increase ofthe rotational speeds to the rotational speeds for the filled rollingmill is effected uniformly at all stand locations through which thefront section of the tubular material passes.

3. A method as defined in claim 2, wherein the rotational speeds of thestand locations through which the front section of the tubular materialpasses are respectively increased such that they attain the samepercentage speed reduction as the last stand location rolling the frontsection of the tubular material.

4. A method of rolling down tubular material in a rolling mill in whichthe rolls of consecutive stands normally operate with graduallyincreasing rotational speed, wherein with the rolling mill filled theroll speeds of all stands, p in number, participating in the deformationof the tubular material are reduced relative to the speed sequenceemployed for rolling the central section of the tubular material, thepercentage rotational speed reduction at all stands being equal, andwherein subsequently upon entry of the rear section of the tubularmaterial is consecutive stands 1 through n of the rolling mill thereduced speeds of the stands 2 through p are increased dependent on thepassing of the rear section of the tubular material through the stands 1through n such that in the vicinity of the rear section of the tubularmaterial the percentage rotational speed reduction decreases with anincreasing stand location number up to the stand location n, and whereinthe central section of the tubular material is rolled in stands thepercentage rotational speed reduction of which is equal.

5. A method as defined in claim 4, wherein the percentage increase ofthe rotational speeds of the stands which roll the central section ofthe tubular material is effected uniformly.

6. A method of rolling down tubular material in a rolling mill in whichthe rolls of consecutive stands normally operate with graduallyincreasing rotational speed, wherein upon entry of the rear section ofthe tubular material in consecutive stands 1 through q the associatedroll rotational speeds thereof are reduced dependent on the passing ofthe rear section of the tubular material through these stands such thatin the vicinity of the rear section of the tubular material thepercentage rotational speed reduction decreases with an increasing standlocation number and wherein the central section of the tubular materialis rolled in stands with unaltered rotational speeds.

7. A method as defined in claim 6, wherein the percentage rotationalspeed reduction of the stand group respectively rolling the rear sectionof the tubular material is effected uniformly.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,645,121 DATED February 1972 INVENTOR(S) Gerd Pfeiffer andHorst Biller It is certified that error appears in the above-identifiedpatent and that said Letters Patent is hereby corrected as shown below:

The title page, add the following to [30] Foreign Application PriorityData:

-- May 31, 1969 Germany l9 27 879 T May 31, 1969 Germany '19 27 880; 1

Signed and Scaled this Seventeenth D a y 0 February I 98] |SEA L .4nest:

RENE D. TEGTMEYER Arresting Oflicer Acting Commissioner of Patents andTrademarks mg? UNITED STATES PA'IENT OFFICE CERTIFICATE OF CORRECTION TPatent No. 3 ,645 ,121 ba ted Feb. 29, 1972 Inventor(s) Gerd Pfeiffer eta-l'.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

-C In the Drawings: Cancel Figure 7 and renumber Figfire 8 as Figure 7.,I

Signedend seel ed this 131 1 day or June 1972.,-

(SEAL) A ttes t:

EDWARD M.FLE'ICHER J'Ro-' ROBERT S H K Attesting- Officer I Commissionerof Patents

1. A method of rolling down tubular material in a rolling mill in whichthe rolls of consecutive stands normally operate gradually increasingrotational speed, which comprises: a stepwise reduction of therotational roll speedS at a plurality of roll stands prior to entry ofthe front section of the tubular material, the percentage of therotational speed reduction being at a maximum at the first standlocation and decreasing at the subsequent stands; and subsequently, uponentry of the front section of the tubular material into the rollingmill, an increase in speed of the individual stand locations, dependenton the passing of such front section through a plurality of standlocations, to the rotational speed sequence for a filled rolling mill,so that the normally thickened front section of the tubular material issubstantially shortened.
 2. A method as defined in claim 1, wherein thepercentage increase of the rotational speeds to the rotational speedsfor the filled rolling mill is effected uniformly at all stand locationsthrough which the front section of the tubular material passes.
 3. Amethod as defined in claim 2, wherein the rotational speeds of the standlocations through which the front section of the tubular material passesare respectively increased such that they attain the same percentagespeed reduction as the last stand location rolling the front section ofthe tubular material.
 4. A method of rolling down tubular material in arolling mill in which the rolls of consecutive stands normally operatewith gradually increasing rotational speed, wherein with the rollingmill filled the roll speeds of all stands, p in number, participating inthe deformation of the tubular material are reduced relative to thespeed sequence employed for rolling the central section of the tubularmaterial, the percentage rotational speed reduction at all stands beingequal, and wherein subsequently upon entry of the rear section of thetubular material is consecutive stands 1 through n of the rolling millthe reduced speeds of the stands 2 through p are increased dependent onthe passing of the rear section of the tubular material through thestands 1 through n such that in the vicinity of the rear section of thetubular material the percentage rotational speed reduction decreaseswith an increasing stand location number up to the stand location n, andwherein the central section of the tubular material is rolled in standsthe percentage rotational speed reduction of which is equal.
 5. A methodas defined in claim 4, wherein the percentage increase of the rotationalspeeds of the stands which roll the central section of the tubularmaterial is effected uniformly.
 6. A method of rolling down tubularmaterial in a rolling mill in which the rolls of consecutive standsnormally operate with gradually increasing rotational speed, whereinupon entry of the rear section of the tubular material in consecutivestands 1 through q the associated roll rotational speeds thereof arereduced dependent on the passing of the rear section of the tubularmaterial through these stands such that in the vicinity of the rearsection of the tubular material the percentage rotational speedreduction decreases with an increasing stand location number and whereinthe central section of the tubular material is rolled in stands withunaltered rotational speeds.
 7. A method as defined in claim 6, whereinthe percentage rotational speed reduction of the stand grouprespectively rolling the rear section of the tubular material iseffected uniformly.